For Maps, Check your valve content, copy them to usermod/Maps (better find the models and materials for them and copy them to the usermod/models and usermod/materials folders. If they give you an HDR error, search this discussion group for recommended fixes. If you don't own any valve content then you have to create your own if you want custom maps.

Once you find your custom content, I have a few video tuts on my Youtube channel to tell you how to get them in to SFM.